This application claims priority under 35 U.S.C. xc2xa7119 to Japanese patent application no. 11-152239 filed May 31, 1999.
1. Field of the Invention
The present invention relates to a method of producing a blank used for manufacturing a single-headed piston, and more particularly to techniques for reducing the weight of the blank.
2. Discussion of the Related Art
A single-headed piston is used in a swash plate type compressor, as described in JP-A-9-256952, for example. The single-headed piston disclosed in this publication includes a head portion, and a neck portion formed integrally with the head portion. The head portion is axially movably fitted in a cylinder bore formed in a housing of the compressor, while the neck portion engages the opposite surfaces of a swash plate of the compressor through a pair of shoes such that the swash plate is movable relative to the neck portion, so that the single-headed piston is reciprocated by rotation of the swash plate to effect suction and compression of a gas.
The publication identified above proposes a method of producing two single-headed pistons from one blank. The method includes steps of: forming by casing or forging a blank wherein two neck portions for the two single-headed pistons are integrally formed in series arrangement in the axial direction of the blank; machining the outer circumferential surfaces of head portions and the other portions of the blank; applying a coating to the outer surface of the starting blank; grinding the outer circumferential surfaces of the head portions; cutting the starting blank into two pieces, namely, the two single-headed pistons. In this method, the blank consists of two sections which correspond to the respective two single-headed pistons and whose neck portions are arranged in series connection with each other in the axial direction, so that the productivity of the blank per se is improved. In addition, the method permits easy and efficient machining, coating (e.g., forming a polytetrafluoroethylene film) and other operations to be performed on the blank, since these operations are performed simultaneously on the two sections of the blank for the respective two single-headed pistons. Further, the method permits easy and stable grinding operations on the outer circumferential surfaces of the two head portions, by a centerless grinder, since the blank has a sufficiently large distance between the two head portions.
JP-A-10-159725 proposes a method of producing a single-headed piston which uses a hollow head portion, for the purpose of reducing the weight of the piston. Described in detail, the head portion includes a cylindrical container portion which is closed at one of its opposite ends and open at the other end, and a closure member which closes the open end of the cylindrical container portion. The open end of the container portion is closed by first fitting the closure member in the opening of the container portion and then fixing the closure member in the opening by calking the edge of the open end. This single-headed piston, whose head portion is hollow, has a reduced weight. Although the piston consists of two members one of which includes the neck portion and the container portion and the other of which is the closure member, there is not a risk that the closure member is removed upon compression of the gas by the piston, since a force produced by compression of the gas acts on the closure member in a direction that causes the closure member onto the container portion. During reciprocation of the single-headed piston, an inertial force acts on the closure member in a direction that causes the closure member to be moved away from the container portion. However, there is not a risk that the closure member is removed from the container portion, since the mass of the closure member is small and the inertial force is accordingly small. The single-headed piston receives a side force from the swash plate during the reciprocation, in a direction perpendicular to the direction of reciprocation. But, a bending moment based on this side force is small at the position of the closure member, and therefore there is not a risk that the closure member is removed due to the bending moment.
However, the blank for the single-headed pistons used in the method disclosed in JP-A-9-256952 is heavy, and it is difficult to reduce the weight of each single-headed piston produced according to this method. On the other hand, the method disclosed in JP-A-10-159725 has a risk that the closure member is rotated relative to the cylindrical container portion during an operation to machine the outer circumferential surface of the blank after the closure member is fixed to the container portion by calking. JP-9-256952 teaches the provision of a holding portion on the closure member, as an example of chucking means for the blank, so that the blank is chucked at the holding portion for transmitting a torque to the blank for rotating the blank during the machining operation. However, the force by which the closure member is fixed to the container portion by calking is not sufficient to withstand the torque applied to the closure member, whereby the closure member may be rotated relative to the container portion, causing the blank to be damaged.
Although the methods described above apply to the compressors of swash plate type in which the neck portion of the piston engages the opposite surfaces of the swash plate through the shoes, problems similar to those described above may be encountered with respect to a method of producing a blank for the single-headed piston used in compressors other than the swash plate type, such as wave cam type compressors. The term xe2x80x9csingle-headed pistonxe2x80x9d used herein is collectively used to mean single-headed pistons used not only in the swash plate type compressors but also the other types of compressors. Accordingly, the term xe2x80x9cneck portionxe2x80x9d of the piston means a portion of the single-headed piston at which the piston engages a driving member or device.
The present invention was made in the light of the background prior art described above. It is a first object of the present invention to provide a method of producing a blank which permits easy manufacture of a hollow single-headed piston having a reduced weight. It is a second object to provide such a blank.
The first or second object indicated above may be achieved according to any one of the following forms or modes of the present invention, each of which is numbered like the appended claims and depends from the other form or forms, where appropriate, to indicate and clarify possible combinations of technical features of the present invention, for easier understanding of the invention. It is to be understood that the present invention is not limited to the technical features and their combinations described below. It is also to be understood that any technical feature described below in combination with other technical features may be a subject matter of the present invention, independently of those other technical features.
(1) A method of producing a blank for manufacturing a single-headed piston including a head portion and a neck portion which is formed integrally with the head portion, for engagement with a drive member, the method comprising the steps of: manufacturing a body member including a twin neck section and two cylindrical hollow head sections formed integrally with the twin neck section such that the two hollow head sections extend from opposite ends of the twin neck section, the twin neck section consisting of two portions which are mutually integrally formed in series with each other and which correspond to the neck portions of respective two single-headed pistons, each of the two hollow head sections being open at at least one of opposite ends thereof which is remote from the twin neck section; manufacturing two closing members each for closing an open end of a corresponding one of the two hollow head sections; and fixing each of the two closing members to the body member, so as to close the open end of the corresponding hollow head section.
According to the method according to the above form (1) of this invention, it is possible to produce a blank from which two single-headed pistons each including a lightweight head portion of hollow structure can be manufactured. Accordingly, the present method provides an advantage of facilitating operations to machine and coat the outer circumferential surfaces of the hollow head sections of the blank, and centerless grinding operations on those outer circumferential surfaces. Further, the blank consists of the integral body member the length of which is substantially the same as that of the blank, and the two closing members which are fixed to the respective opposite ends of the body member. This blank has a higher degree of dimensional accuracy with a reduced adverse influence by the accuracy of fixing of the closing members to the body member, and permits a reduction in the required amount of stock removal by the machining operation, as compared with a blank which consists of a twin neck section and two hollow head sections bonded to the respective opposite ends of the twin neck section. In addition, the amount of stock removal from the present blank in the machining operations is not restricted by a bending moment due to a cutting resistance inevitably generated in the machining operations, since the blank does not have any point of fixing or bonding of two sections thereof to each other, at the portion of the blank at which the bending moment is comparatively large. Consequently, the machining efficiency of the present blank can be easily improved. It is further noted that since the closing members of the present blank are fixed to the respective opposite ends of the body member, the closing member is located at one end of each single-headed piston manufactured from the present blank, so that a relatively small amount of positional error or deformation at the point of fixing of the closing member to the other portion of the piston will not have a significant influence on the dimensional accuracy of the single-headed piston even if such positional error or deformation takes place on the manufactured single-headed piston.
(2) A method according to the above form (1), wherein each closing member is formed such that each closing member includes a fitting portion having an outer circumferential surface to be fitted in an inner circumferential surface of the corresponding hollow head section, and each closing member and the body member are formed such that one of the outer circumferential surface of the fitting portion and the inner circumferential surface of the corresponding hollow head section has a projecting portion formed thereon so as to extend in an axial direction of the fitting portion and the corresponding hollow head section, while the other of the outer circumferential surface and the inner circumferential surface has a recessed portion for engagement with the projecting portion, the step of fixing each of the two closing members to the body member comprising fitting the fitting portion of each closing member in the corresponding hollow head section of the body member at the outer and inner circumferential surfaces while effecting engagement of the projecting and recessed portions with each other, to thereby prevent relative rotation of the body member and each closing member.
In the above form (2) of the present invention, each closing member is fitted at its outer circumferential surface in the inner circumferential surface of the body member, making it relatively easy to assure a high degree of concentricity of the closing member and the body member, thereby permitting the blank to have a high degree of dimensional accuracy as a whole. In addition, the relative rotation of each closing member and the body member is prevented by the engagement of the projecting and recessed portions with each other, facilitating the machining operation on the blank. For instance, each closing member may have a holding portion which extends from a central part of the outer end face remote from the body member, so that the blank is held by a suitable chuck at the holding portion of each closing member at each end of the blank. To perform the machining operation on the outer circumferential surfaces of the hollow head sections of the blank, the blank held by the chucks at the holding portions of the two closing members is rotated to machine the outer circumferential surfaces of the hollow head sections. In this case, the closing members and the body members are effectively prevented from being rotated relative to each other, by the mutually engaging projecting and recessed portions provided on one and the other of each closing member and the hollow head section. Accordingly, the machining operations can be effected with high efficiency.
The projecting portion includes at least one projection, while the recessed portion includes at least one recess. Preferably, the circumferential dimension of the projecting portion as measured in the circumferential direction of the closing member and the hollow head section is slightly larger than that of the recessed portion, so that the projecting and recessed portions engage each other with an interference fit therebetween, which is effective to assure complete prevention of the relative rotation of the body member and the closing member. Further, the interference fit between the projecting and recessed portions improves the strength of bonding of the closing member to the body member, making it possible to eliminate the need of establishing an interference fit between the outer circumferential surface of the fitting portion of the closing member and the outer circumferential surface of the hollow head section, or making it possible to reduce the required amount of interference between those outer and inner circumferential surfaces. Accordingly, the radially outward expansion of the hollow head section due to the interference fitting of the closing member in the hollow head section can be avoided, or the amount of that expansion can be reduced. As a result, the required amount of stock removal from the blank in the machining operations on the outer circumferential surfaces of the hollow head sections can be reduced, for example, and the required machining time can be accordingly reduced. In addition, the reduction of the strength of the stock due to the stock removal can be minimized.
(3) A method according to the above form (2), wherein at least one of the projecting and recessed portions has a guide portion at one end thereof at which the engagement of the projecting and recessed portions is initiated, the guiding portion being shaped to guide the projecting portion into the recessed portion.
The guiding portion permits smooth engagement of the projecting and recessed portions with each other. The guiding portion is effective particularly where the engagement of the projecting and recessed portions is effected with an interference fit therebetween.
(4) A method according to the above form (2) or (3), wherein the projecting portion is shaped such that a circumferential dimension of the projecting portion as measured in a circumferential direction of each closing member and the corresponding hollow head section increases in the axial direction from one end of the projecting portion at which the engagement of the projecting and recessed portions is initiated, toward the other end of the projecting portion.
In the method according to the above form (4), the recessed portion may have a constant circumferential dimension, or may alternatively be tapered with the circumferential dimension increasing with an increase in the circumferential dimension of the projecting portion.
Preferably, the circumferential dimension of the projecting portion at its end at which the engagement of the projecting and recessed portions is initiated is smaller than that of the recessed portion at its end at which the engagement is initiated. The shaping of the projecting portion according to the above form (4) is also effective particularly where the engagement of the projecting and recessed portions is effected with an interference fit therebetween, since the projecting portion can be easily press-fitted into the recessed portion.
(5) A method according to the above form (1), wherein each closing member is formed such that each closing member includes a fitting portion having an outer circumferential surface to be fitted in an inner circumferential surface of the corresponding hollow head section, and each closing member and the body member are formed such that one of the outer circumferential surface of the fitting portion and the inner circumferential surface of the corresponding hollow head section has a projection portion, while the other of the outer circumferential surface and the inner circumferential surface has a recessed portion for engagement with the projecting portion, the projecting and recessed portions being shaped such that the projecting portion is snapped into the recessed portion, with elastic deformation of at least one of the hollow head section and the fitting portion of each closing member in a radial direction thereof, and such that the engagement of the projecting and recessed portions prevents a relative movement thereof in a circumferential direction of the fitting portion and the corresponding hollow head section.
The recessed portion of the blank produced according to the above form (5) of the invention is dimensioned such that the recessed portion can accommodate the projecting portion in the axial and circumferential directions of the fitting portion of the closing member and the hollow head section. The elastic deformation of at least one of the hollow head section and the fitting portion takes place only when the fitting portion is fitted in the hollow head section while the projecting and recessed portions are brought into engagement with each other. After the projecting portion is snapped into the recessed portion, the above-indicated at least one of the hollow head section and the fitting portion is restored to its original state without elastic deformation. The engagement of the surfaces of the projecting and recessed portions which are perpendicular to the axial direction of the body member prevents removal of each closing member from the body member, while the engagement of the surfaces of the projecting and recessed portions which are parallel to the axial direction prevents relative rotation of the closing member and the body member.
At least one of the hollow head portion of the body member and the fitting portion of the closing member may have a cutout or cutouts or other means for facilitating the elastic deformation of the above-indicated at least one of the hollow head section and the fitting portion. For instance, the fitting portion of the closing member may be an annular fitting portion which has the projecting or recessed portion in the form of at least one projection or recess. In this case, the annular fitting portion may further have two cutouts formed on the circumferentially opposite sides of each projection or recess such that the cutouts have a depth from the annular end face of the annular fitting portion in the axial direction of the annular fitting portion, and are formed through the annular wall of the annular fitting portion in the radial direction. Alternatively, at least one of the outer circumferential surface of the annular fitting portion and the inner circumferential surface of the hollow head section has cutouts formed on the circumferentially opposite sides of each projection or recess. In the former case, when each part of the annular wall the elastic deformation of each part of the annular wall of the annular fitting portion which is located between the two cutouts is facilitated by the two cutouts. In the latter case where the cutouts are formed in at least one of the annular fitting portion and the hollow head section, when the parts of the other of the fitting portion and the hollow head section in which the projecting or recessed portion is formed are elastically deformed in the radial inward or outward direction, the cutouts permit elastic deformation in the opposite radial direction of the other parts of the above-indicated other of the fitting portion and the hollow head section, which other parts are circumferentially adjacent to the above-indicated parts. Thus, the elastic deformation of the above-indicated other of the fitting portion and the hollow head section is facilitated by the cutouts.
In the above form (5) of this invention, the fitting portion of each closing member can be fixed to the body member, so as to prevent relative rotation and axial movement of the closing member and the body member.
(6) A method according to the above form (1), wherein each closing member is formed such that each closing member includes a fitting portion having an outer circumferential surface to be fitted in an inner circumferential surface of the corresponding hollow head section, the fitting portion further having as the recessed portion at least one recess which is not continuous in a circumferential direction of the corresponding hollow head section, and the step of manufacturing a body member and the step of fixing each of the two closing members to the body member comprise fitting the fitting portion into the corresponding hollow head section, and forcing at least one part of the corresponding hollow head section corresponding to the at least one recess in a radially inward direction of the corresponding hollow head section by plastic deformation, to form as the projecting portion at least one projection which engages the at least one recess, respectively.
In the method according to the above form (6) of this invention, the at least one projection forced out so as to extend from the inner circumferential surface of the hollow head section of the body member is held in engagement with the at least one recess formed in the outer circumferential surface of the fitting portion of the closing member, so that the closing member can be fixed to the body member so as to prevent relative rotation and axial movement of the closing member and the body member.
(7) A method according to the above form (1), wherein each closing member is formed such that each closing includes a fitting portion having an outer circumferential surface to be fitted in an inner circumferential surface of the corresponding hollow head section, and the step of manufacturing a body member and the step of manufacturing two closing members comprise forming a multiplicity of projections on each of at least one of the outer circumferential surface of the fitting portion and the inner circumferential surface of the corresponding hollow head section over an entire circumference thereof, the step of fixing each of the two closing members to the body member comprising fitting the fitting portion in the inner circumferential surface of the corresponding hollow head section such that the multiplicity of projections formed on each of the at least one of the outer and inner circumferential surfaces are held in forced engagement with the other of the outer and inner circumferential surfaces, with an interference therebetween.
(8) A method according to the above form (7), wherein the multiplicity of projections are formed by knurling the at least one of the outer and inner circumferential surfaces over the entire circumference.
(9) A method according to the above form (7), wherein the multiplicity of projections are formed by serrating the at least one of the outer and inner circumferential surfaces over the entire circumference.
(10) A method according to any one of the above forms (1)-(9), wherein the step of fixing each of the two closing members comprises bonding each closing member to the body member by an adhesive agent.
Although only the bonding of the closing member to the body member by an adhesive or bonding agent permits the fixing of the closing member to the body member so as to prevent relative rotation and axial movement of the closing member and the body member, the arrangement according to any one of the above forms (2)-(9) together with the bonding assures complete prevention of the relative rotation and axial movement of the closing member and the body member. This also applies to the method according to the following forms (11) and (12).
(11) A method according to any one of the above forms (1)-(9), wherein the step of fixing each of the two closing members comprises bonding each closing member to the body member by an alloy having a melting point lower than those of the closing member and the body member.
(12) A method according to any one of the above forms (1)-(9), wherein the step of fixing each of the two closing members comprises welding each closing member to said body member.
The welding may be effected by various methods such as electron beam welding and laser beam welding, and at a reduced pressure or the atmospheric pressure. For instance, the electron beam welding may be effected at a reduced pressure, to avoid air expansion due to heat and to eliminate a need of evacuating the interior of the body member closed by the closing members, and a need of providing the piston with an air vent.
(13) A blank for manufacturing a single-headed piston including a head portion and a neck portion which is formed integrally with the head portion, for engagement with a drive member, the blank comprising: a body member including a twin neck section and two cylindrical hollow head sections formed integrally with the twin neck section such that the two hollow head sections extend from opposite ends of the twin neck section, the twin neck section consisting of two portions which are mutually integrally formed in series with each other and which correspond to the neck sections of two single-headed pistons, each of the two hollow head sections being open at at least one of opposite ends thereof which is remote from the twin neck section; and two closing members fixed to the body member such that each of the two closing members closes an open end of a corresponding one of the two hollow head sections.
The blank according to the above form (13) of this invention may have any one of the features included in the above forms (2)-(12) of the invention.
The above form (13) of the present invention has substantially the same advantages as described above with respect to the method according to the above form (1) of the invention. Where the blank includes any one of the features of the above forms (2)-(12), the blank provides the substantially the same advantages as described above with respect to those forms (2)-(12) of the invention.
(14) A method of producing a blank for manufacturing a single-headed piston including a head portion and a neck portion which is formed integrally with the head portion, for engagement with a drive member, the method comprising the steps of: manufacturing a body member including a neck section and a hollow head section which is formed integrally with the neck section and which is open at one of opposite ends thereof which is remote from the neck section, the body member having one of a projecting portion and a recessed portion; manufacturing a closing member for closing an open end of the hollow head section, the closing member having the other of the projecting and recessed portions; and fixing the closing member to the body member such that relative rotation of the body member and the closing member is prevented by engagement of the projecting and recessed portions.
The method according to the above form (14) of this invention may have any one of the features included in the above forms (3)-(11) of the invention.
The method according to the above form (14) has substantially the same advantages as described above with respect to the above forms (1) and (2), except for the advantage relating to the manufacture of two single-headed pistons from the single blank. Where the present method includes any one of the features of the above forms (3)-(11), the method provides substantially the same advantages as described above with respect to those forms (3)-(11) of the invention. The same applies to the following form (15) of the invention.
(15) A blank for manufacturing a single-headed piston including a head portion and a neck portion which is formed integrally with the head portion, for engagement with a drive member, the blank comprising: a body member including a neck section and a hollow head section which is formed integrally with the neck section and which is open at one of opposite ends thereof which is remote from the neck section, the body member having one of a projecting portion and a recessed portion; and a closing member which closes an open end of the hollow head section and which has the other of the projecting and recessed portions, the closing member being fixed to the body member such that relative rotation of the body member and the closing member is prevented by engagement of the projecting and recessed portions.
The blank according to the above form (15) of this invention may include any one of the features of the above forms (3)-(11).